1. Field of the Invention
This invention relates generally to devices for the production of drip irrigation tubes, and more particularly to devices for the production of drip irrigation tubes having metering elements.
2. Description of Related Art
Drip irrigation tubes are used for well-targeted direct irrigation of crops. These drip irrigation tubes can be designed to be on the surface in the vicinity of the plants or can be sunk into the ground. Disposed in the region of the individual plants can be one or more metering elements, by means of which it is made possible for the water to be able to escape dropwise through a bore made in the walling of the tube. In irrigation employing drip irrigation tubes of this kind, water can be used very sparingly and efficiently.
Devices for production of drip irrigation tubes are known in diverse designs. A device for production of drip irrigation tubes is shown in EP A 0 715 926, for example, in which a tube body is extruded by an extrusion apparatus. This extruded tube body is formed to the desired diameter and cooled. Pushed into the tube body are metering elements which are pressed onto the walling of the tube and are welded together therewith. The tube body provided with these metering elements arrives in a drilling device, in which the tube walling is provided with one continuous bore in each case in the vicinity of the metering elements, through which bore the water is able to escape dropwise during the irrigation process, metered by the metering element. Afterwards the drip irrigation tube thus produced can be wound up for further transport, for example on a winding device.
During manufacture of such drip irrigation tubes, the making of the outlet holes for the water by the drilling device must take place with precise positioning with respect to the corresponding metering elements. With the known device described above, the drilling of the outlet hole in the tube body is carried out after passage through the cooling devices. This means that this procedural step takes place a relatively long time after the insertion of the metering elements into the extruded tube body and the connection of these metering elements to the walling of the tube body. In particular with thick-walled tubes, the position of the respective metering element inside the tube body can be easily determined by monitoring the pressing pressure of the roller on the outside of the tube walling in the region of connection of the metering element to the walling or the evasive movement of the roller during passage of a metering element. A corresponding signal is emitted to the drilling device; the execution of the drilling takes place with time delay, however, depending upon the speed of passage of the tube body and the distance between drilling device and pressing roller, it being possible for mistakes to result, for instance owing to a change in length of the tube body as a result of higher tensile load.
Furthermore the bore is made in the completely hardened and cooled-off tube body.